Currently, there are several methods defined by the Third Generation Partnership Project (3GPP) related to data offloading: Local Internet Protocol Access (LIPA), Selected Internet Protocol Traffic Offload (SIPTO) and Internet Protocol Flow Mobility (IFOM).
IFOM is a method where a UE has data sessions with the same Packet Data Network (PDN) connection simultaneously over a 3GPP network and a WiFi network. A PDN Connection is an association between a UE and a PDN, represented by an Internet Protocol (IP) address. A PDN is identified by an Access Point Name (APN). Based on the scenario, the UE could add or delete data sessions over either of the network accesses, effectively offloading data. While the data offload is largely transparent to the UE in LIPA and SIPTO, the logic to offload data is more UE centric in IFOM and largely transparent to the Radio Access Network (RAN). Network Based-IFOM (NB-IFOM, NBIFOM) is a variant of IFOM which relates to IP Flow Mobility using network-based mobility protocols (e.g. on the S2a and S2b interface via the General packet radio service Tunneling Protocol (GTP) mobility and using a Proxy Mobile IPv6 (PMIP) mobility procedure). Network based IFOM is contrary to client based IFOM which relates to the S2c interface via a Dual-stack Mobile IPv6 (DSMIP) procedure.
SIPTO is a method where portions of the IP traffic on a Home (evolved) NodeB (H(e)NB) or a cellular network is offloaded to a local network, in order to reduce the load on the system. The target network entity could be a H(e)NB or another gateway in the cellular network that is geographically closer located to the UE. SIPTO can be triggered by events like UE mobility, special occasions that leads to concentration of traffic or other network rules. The basic idea of SIPTO is to select a Serving Gateway (SGW) and a PDN GateWay (PGW) topologically and geographically closer to the radio network (for both Fourth Generation (4G) and Third Generation (3G) networks) and to the Mobility Management Entity (MME), and to use them to offload data.
FIG. 1 illustrates an example of IFOM. FIG. 1 illustrates an EPC core network 100a. EPC is short for Evolved Packet Core. In FIG. 1, the UE 101 is adapted to be served by a base station 103 in the EPC core network 100a. 
The UE 101 may be a device by which a subscriber may access services offered by an operator's network and services outside operator's network to which the operators radio access network and core network provide access, e.g. access to the Internet. The UE 101 may be any device, mobile or stationary, enabled to communicate in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device, Device to Device (D2D) device, Internet of Things (IoT) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The UE 101 may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another UE or a server.
The base station 103 may represent a 3GPP network. The base station 103 may be referred to as e.g. evolved Node B (eNB), eNodeB, NodeB, B node, Radio Base Station (RBS), Base Transceiver Station (BTS), Radio Network Controller (RNC) depending on the technology and terminology used. The base station 103 is adapted to communicate over an air interface operating on radio frequencies with the UEs 101 within range of the base station 103.
The EPC core network 100a comprises core network nodes such as a SGW 105, a PGW 108 and a MME 110. The EPC core network 100a may comprise additional core network nodes which are not illustrated in FIG. 1. The base station 103 is adapted to be connected to both the SGW 105 and the MME 110. The MME 110 and the SGW 105 are adapted to be connected to each other. The SGW 105 is adapted to be connected to the PGW 108.
The SGW 105 is a gateway which is adapted to e.g. routes and forwards user data packets, while also acting as the mobility anchor for a user plane during inter-eNB handovers and as the anchor for mobility between Long Term Evolution (LTE) and other 3GPP technologies.
The PGW 108 is a gateway which terminates an interface towards the PDN (not illustrated in FIG. 1). If the UE 101 is accessing multiple PDNs, there may be more than one PGW 108 for that UE 101. Functions of the PGW 108 are e.g. providing connectivity from the UE 101 to external PDNs by being the point of exit and entry of traffic for the UE 101, performing policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening etc. The PGW 108 may be co-located with a Home Agent (HA). This may also be described as the HA functionality is implemented in the PGW 108. Such co-located node may be referred to as a HA/PGW. According to the 3GPP, the HA is a mobile Internet Protocol version 4 (IPv4) router on a UE's 101 home network which tunnels datagrams for delivery to the UE 101 while it is registered on a visited network. The term HA mentioned above may be described as a router which maintains information about the UEs 101 current location. The reference number 108 will also be used for referring to the co-located HA/PGW node. The PGW part of the HA/PGW 108 or the standalone PGW 108 is a gateway or gateway functionality which is arranged to act as an anchor between the 3GPP access and the non-3GPP access 115, it provides connectivity from the UE 101 to the PDN etc.
The SGW 105 and the PGW 108 may be implemented in one common physical node or in separate physical nodes.
The MME 110 is a core network node having functions such as e.g. Non-Access Stratum (NAS) signalling, Inter Core Network (CN) node signalling for mobility between 3GPP access networks, UE reachability, Tracking Area (TA) list management, PGW and SGW selection, MME selection for handover with MME change etc. The MME 110 may be a standalone MME node or it may be a combined MME and Serving General packet radio service Support Node (SGSN) node, i.e. a node where the MME and SGSN are co-located. In the following, the abbreviation MME may refer to a standalone MME or a combined MME and SGSN node. The reference number 110 is used for referring to the standalone MME and to the combined MME and SGSN node.
FIG. 1 also illustrates a non-3GPP network 115. The non-3GPP network 115 (or nodes in the non-3GPP network 115) may be adapted to be connected to the PGW 108 in the EPC core network 100a, i.e. the PGW 108 is adapted to be connected to both the SGW 105 and the non-3PGP network 115. The non-3GPP network 115 may be for example a WiMAX network, CDMA 2000 network, Wireless Local Area Network (WLAN) or a fixed network. The non-3GPP network 115 may be trusted or non-trusted. The trusted and non-trusted versions of the non-3GPP network 115 will be described in more detail later.
The two arrows seen in FIG. 1 represent PDN connections for the UE 101. The left arrow represents the PDN connection via the 3GPP network and the right arrow represents the PDN connection via the non-3GPP network 115. Both the PDN connection via the 3GPP network and the PDN connection via the non-3GPP network 115 are for the same APN.
FIG. 2 illustrates an example of SIPTO. As depicted in FIG. 2, SITPO in a macro network 100b can have different data paths for a certain service comparing to the one of the UE's 101 regular PDN connection. A macro network 100b may be described as a network that provides radio coverage served by a high power base station. For example, a macro network 100b provides a larger coverage than a micro network. FIG. 2 also illustrates an EPC core network 100a comprising one or more core network nodes. In FIG. 2, the UE 101 is adapted to be served by the base station 103 in the macro network 100b. The base station 103 in FIG. 2 may be for example a high power base station. The interface between the UE 101 and the base station 103 is referred to as an LTE-Uu interface. The base station 103 is connected to the EPC core network 100a via the SGW 105 via a S1-U interface. The SGW 105 is adapted to be connected to two PGWs, i.e. the PGW1 108a and the PGW2 108b, via a respective S5 interface. SGi is the interface between each of the PGWs 108a, 108b and external PDN nodes (not illustrated in FIG. 2). The reference number 108 without a or b refers to any of the two PGWs.
The SGW 105 is also adapted to be connected to the MME 110 via a S11 interface. The MME 110 is also adapted to be connected to the base station 103 via a S1-MME interface. The SGW 105, the PGW1 108a, the PGW2 108b and the MME 110 are core network nodes which are comprised in the EPC core network 100a. A regular data path is illustrated with a solid arrow in FIG. 2, and is a data path that goes via the PGW2 108b. The SIPTO data path is illustrated with a dotted arrow in FIG. 2, and is a data path that goes via the PGW1 108a. 
It is also possible that the EPC core network (e.g. the SGSN/MME 110 or any other suitable node in the EPC core network 100a) determines to relocate the PGW 108 when UE 101 is connected to the 3GPP access and moving within/between Public Land Mobile Networks (PLMNs). Some operators in e.g. China require such kind of “local breakout” for its national roaming subscribers. The PDN disconnection is similar to SIPTO, but the decision to change the PGW 108 is implementation specific. By changing the PGW 108, the UE 101 can have a better user plane optimization (e.g. a PGW 108 closer to the UE 101 location), and also with a correct dialing plan and charging for Voice over LTE (VoLTE) call.
As soon as the SGSN/MME 110 determines to relocate the PGW 108 for the UE 101, it transmits a PDN Deactivation Request message (with reactivation required) or a Detach message (with re-attach required) to the UE 101. Thereby the UE 101, as per standard stipulated, will re-establish the PDN connection to the EPC, i.e. the connection to the 3GPP network and the new PGW 108 will then be used.
FIG. 3 depicts the PGW 108 relocation as the UE 101 moves from one to another location. The UE 101 moves from being served by the base station1 103a to being served by the base station2 103b. The reference number 103 without the letters a and b refers to any of the base stations. Both base stations 103a, 103b are connected to the same MME 110 in the EPC core network 100a. Before the UE 101 moves, the PGW1 108a is used for data transmission. The data path before the movement is indicated with a dotted arrow in FIG. 3. After the UE 101 has moved, the PGW2 108b (the PGW2 108b is topologically/geographically closer to the UE 101 compared to the PGW1 108a) is chosen for an optimized data transmission. The data path after the movement is indicated with a solid arrow in FIG. 3.
As stipulated by 3GPP, all simultaneous active PDN connections of a UE 101 that are associated with the same APN shall be provided by the same PGW 108.
When IFOM is used for a UE 101 utilizing both non-3GPP network 115 (trusted or untrusted) and 3GPP network in the context of EPC, and a HA is collocated with the PGW 108, the relocation of the PGW 108 (PGW 108 does not release the resources for another access) will lead to that a different PGW 108 is used for the same APN. This is not allowed since the PGW 108 is the IP anchor point in the PDN network regardless of which access network that is used. Therefore, by such blindly PGW relocation, the old PGW 108 still has the hanging resources, an unexpected behavior might happen in the UE 101 and the remote server of an external PDN due to change of IP address.